I try to do a communication with the esp8266 and Arduino nano since few days, but nothing happens. I've tested many sketches, solution... I've used uart (0,1) from Arduino or SoftwareSerial on multiple I/O but not working.

I also use external voltage ...

When I send AT command directly in the serial monitor It work fine!

So why when I send AT command with the Arduino, the esp8266 doesn't send a response?

I try to do a communication with the esp8266 and Arduino nano since few days, but nothing happens. I've tested many sketches, solution... I've used uart (0,1) from Arduino or SoftwareSerial on multiple I/O but not working.

I also use external voltage ...

When I send AT command directly in the serial monitor It work fine!

So why when I send AT command with the Arduino, the esp8266 doesn't send a response?

I'm total Lost...

No ... When I test

Serial.println("AT");

[Prints data to the serial port as human-readable ASCII text followed by a carriage return character (ASCII 13, or '\r') and a newline character (ASCII 10, or '\n').]